A second group of Amazonian Indians who have never before had contact with the outside world have emerged near the border withBrazil andPeru, heightening fears that the uncontacted tribes are being forced from their land and threatened with extinction.

The group of 24 men, women and children approached Brazilian government officials, reportedly after fleeing attacks in Peru. They are now resting at a Brazilian government base on the Xinane river – an area which is known for its smuggling routes between the two countries.

Settled relatives of the uncontacted tribe said that they were concerned about the forest-dwelling people leaving their homes.

"I'm sad to see that my uncontacted relatives are threatened with extermination, and that Peru has failed to take responsibility," said Nixiwaka Yawanaw, an Amazon Indian from Acre state. "Both the Brazilian and Peruvian authorities must provide the necessary funds to protect them, while there is still time, otherwise one more innocent people will be wiped out in full view of the international public."

According to FUNAI, Brazil's indigenous authority, 77 of these uncontacted tribes are in the Amazon.

The latest emergence of the tribal members comes less than two months after seven Indians from the same tribe made contact with a settled Ashaninka indigenous community.

They told stories of how they had been attacked in Peru – possibly by loggers or cocaine traffickers.

"The majority of old people were massacred by non-Indians in Peru, who shot at them with firearms and set fire to the houses of the uncontacted," said an interpreter who worked with the first group. "They say that many old people died and that they buried three people in one grave."

The tribes are not just threatened by illegal activities and land grabs. Contact with the outside world can also wipe them out through lack of immunity to common diseases.

"Everyone has neighbours, even when they're some distance away, and they'll know who they are," said Survival International. "If it's another tribe, perhaps also uncontacted, they may or may not have friendly relations with them.

"Some may have been in touch with the colonist society in the past, even in past centuries, and then retreated from the violence which that brought. Some may once have been part of larger tribal groups, and split off and moved away, fleeing contact. Some Amazonian groups even had guns, from intertribal trading, before they'd ever met a non-Indian. Most uncontacted tribes have used some metal tools, which they have found, stolen or traded with their neighbours, for many years or even generations.

"All peoples are changing all the time and always have, including uncontacted tribes. Survival doesn't talk about 'pristine' tribes or cultures. They are not backward or 'Stone Age', they just live differently."

Following the recent contacts, however, over 11,000 people have sent an email calling on Peru and Brazil to protect uncontacted tribes' lands as a matter of urgency.

In March Peruvian and Brazilian authorities signed an agreement to work together to protect the land of uncontacted tribes in this area. But campaigners fear that illegal loggers, drug traffickers and oil and gas companies continue to put uncontacted Indians at extreme risk of violence and diseases.

Stephen Corry, director of Survival International, said on Thursday: "The accounts given by these Indians – of the killing of their relatives, and the burning of their houses – were incredibly disturbing.

"This appears to have taken place on the Peru side of the border, probably at the hands of the illegal loggers and drug traffickers whose presence has been known of for years. What will it take for the Peruvian government to actually protect these tribes' territory properly?"